The invention has been designed for picking olives, so the discussion of the background art and of the specific embodiments is limited to this particular application of the invention.
A known method for picking olives and other fruit is manual labour, whereby fruit is removed from trees by hand picking. This is both time-consuming and costly.
Also known are mechanical shaking devices which apply mechanical vibrations directly to the trunk or branches of an olive tree to remove olives, which may be gathered in a net placed on the ground, or by a vertical net having the shape of an upside down cone surrounding the tree trunk. The mechanical shaking method tends to damage the trees and leads to the unwanted removal of leaves and small branches. Some such methods employ a shaker head attachable to an olive tree-trunk or branch. The shaker head can oscillate with a power of up to 100 horse power and is driven by one or more hydraulic motors which impart rotary motion to eccentric masses. The eccentric masses generally comprise rotatable masses with a high inertia which is difficult to control and slow down. Response times for these machines are also slow. The consequences of component failure may also be dangerous in such machines, especially if the eccentric mass is rotating at the top end of its speed range. Some machines provide for adjustability of the speed of the rotating masses. Such oscillating machines generally apply very complicated oscillations of a single dominant frequency or over a very narrow width of dominant frequencies with little regard for the effect on the tree and its roots, and thus the trees are prone to damage often including substantial removal of leaves and/or twigs of the tree. The construction of these oscillating machines generally involves the shaker head being suspended from a carrying frame by means of chains or springs. Another disadvantage of these methods is that only the ripest olives are removed from the tree. The not so ripe olives, which may constitute as much as 40%-50% of the potential crop, remain attached to the plant. To recover as many of these olives as possible the plant is subjected to further mechanical shaking after one or several weeks have elapsed. Notwithstanding this successive treatment, a 10% to 15% residue of olives remains on the plant. Apart from its relative inefficiency, this method of detaching olives from the tree goes counter to one of the main requirements for making high quality extra virgin olive oil which is the use of the younger, less ripe olives. Under ideal conditions the number of trees cropped by this method can be as high as 40 per hour.
Devices are also used extensively to detach the fruit from the plant by beating action. A variety of devices, based on this principle, are being employed with varying degrees of success. The most popular consist of pneumatically, or electrically, powered combs made of light thin rods. These devices are mounted on the end of a pole. The other end of the pole is held and pulled by an operator in a comb-like motion through the plant's thin branches, which bear most of the fruit, while imparting oscillatory beating to the fruit, leaves and branches in the immediate vicinity of the comb's teeth. The olives are detached from the tree by the device's combined beating and combing action. Although with this method it is possible to remove almost all the fruit from the plant, a significant amount of small branches and leaves also fall to the ground and the bark of the larger branches is damaged in places by the beating action. One additional problem of all beating methods is that the olives do not fall vertically to the ground. A quantity of olives is thrown outside the gathering net placed on the ground around the tree. The resulting loss of crop and the accidental squashing of olives by the operator(s) walking over the gathering nets can reduce the harvest efficiency by as much as 10%-15%. In addition such methods are prone to bruising the olives, and unless the olives are processed for producing olive oil very soon after harvesting, they develop an increased level of acidity. If the level of acidity increases above 0.5%, the producer may no longer label the oil “extra virgin”. Finally, all hand held methods of cropping olives are notoriously slow (one tree per hour per operator) and hence they are only practical for small groves.